The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 101 35 699.4, filed on Jul. 21, 2001, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a process for preparing dry broke of a paper, cardboard or coating machine.
2. Discussion of Background Information
It is known that operating conditions can occur with a paper or cardboard machine where the paper produced during paper production cannot be reeled as a finished web, but has to be removed from the area of the paper machine beforehand as a so-called broke. Something similar can also occur with coating machines in which the paper already produced and dried is provided with a layer called a coating. Even with trouble-free operation, material is constantly accumulating in the form of trimmings which have to be slushed and recirculated into the paper making process. Large amounts of dry broke can also occur during reeling or because certain quality demands of the finished paper were not met. As a rule, the material present as broke contains high-quality fibers and is sorted. It is usually crushed and suspended with water.
As a rule, dry broke is only slightly contaminated and is sorted. For these reasons, the emphasis in the reprocessing processes in the prior art is on the mechanical crushing of the already hardened paper web and its suspension in water. In addition to the actual paper fiber, dry broke also contains a relatively large number of mineral fillers. If dry broke is slushed from coated paper, they come to a considerable extent from the substance applied as coating composition. In general, these fillers should be used again for paper making. They can therefore remain at least in part in the recycled dry broke. The suspension obtained in this manner is then guided into the machine chest from which the stock is removed again to produce this paper grade.
A process is known from EP 0 711 369 B1 in which the filler-containing paper material is fractionated in a complicated manner in several steps in order to concentrate the fillers. They are subsequently dispersed and at least partially reused. DE 19532301 describes a process in which coated dry broke is first slushed and possibly cleaned and deflaked. After another thickening, it is also dispersed in a certain embodiment of the process. The process is complex and essentially aimed at treating the filtrates occurring during thickening.
The present invention provides a process with which it is possible to carry out the preparation of the dry broke without too great an expense or effort, thereby avoiding the problems that could arise due to the abundant fillers, in particular coating colors.
The present invention provides that the dry broke is slushed at a consistency of at least about 15% and no more than about 60% and is thereby mechanically processed by shear forces so that the filler particles contained therein are crushed.
The possibility of being able to process the resulting dry broke as a whole with high shear forces is particularly advantageous. Its consistency is already high enough from the outset, and its dirt content is minimal. Complex fractionating steps which presuppose a dilution can therefore be dispensed with as well as a subsequent thickening. The high shear forces are also mostly useful for treating the fibers contained in the dry broke, as they dissolve fiber lumps and activate the fiber surface, thus preparing for reuse in an optimal way.
The present invention is directed to a process for preparing dry broke in one of a paper, cardboard or coating machine. The process includes diluting the dry broke to a consistency of between about 15 to 60%, and slushing the dry broke with shear forces sufficient to crush filler particles in the dry broke.
According to a feature of the invention, the shear forces can be applied to the dry broke in a kneader pulper. Further, the kneader pulper can include a single-screw grinding machine operated at a solids content between about 20 and 50%. The single-screw grinding machine may include kneading tools, and the shear force can be applied by a mechanical process that includes moving the kneading tools relative to each other at a distance of at least about 10 mm at a speed of no more than about 15 m/sec.
In accordance with another feature of the invention, the dry broke may be slushed in one of a kneader pulper, a disk disperser, and a slushing drum.
Further, the shear forces can be applied to the dry broke in a slushing drum at a solids content of between about 20 and 50%.
According to still another feature of the invention, the shear forces can be applied to the dry broke in a rapid-action disk disperser at a solids content of between about 20 and 50%.
Still further, the shear forces can be produced at a stock temperature of below about 60xc2x0 C.
In accordance with a further feature of the instant invention, a specific energy of at least about 80 kWh/t can be applied to the dry broke during slushing.
According to the invention, a majority of the dry broke can include coated paper and the fillers may include coating colors of the coated paper. The crushing of the fillers can prevent the coating colors from forming agglomerates that interfere with the reuse of the dry broke in the machine.
In accordance with the present invention, between formation of the dry broke and the slushing, the dry broke may not be mechanically processed.
Moreover, between formation of the dry broke and the slushing, the dry broke may not be thickened.
In accordance with a further feature of the invention, the dry broke can be composed of first and second dry broke, and the process may further include slushing the first dry broke into a pumpable suspension, diluting the second dry broke with the pumpable suspension, and jointly slushing the first and second dry broke with shear forces sufficient to crush the filler particles. The first dry broke can be formed under the machine. Further, the first dry broke may be substantially immediately slushed. The amount of first dry broke is less than the amount of second dry broke. Still further, a slusher may be located in direct proximity to the machine, and the process can further include slushing of the first dry broke in the slusher. The slusher may be located underneath the machine. Moreover, the machine can include a receiver vat, and the process may further include storing the pumpable suspension is in the receiver vat. The pumpable suspension can be produced with a consistency of between about 4 and 10%.
Between the formation of the dry broke and the slushing, the process can further include shredding the dry broke.
In accordance with yet another feature of the present invention, the shear forces can grind the filler particles to a grain size of not more than about 60 xcexcm. Further, the shear forces may grind the filler particles to a grain size of not more than 40 xcexcm.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.